Thin walled polynitrile oxide crosslinked rubber film products and methods of manufacture thereof

ABSTRACT

Natural rubber and/or synthetic polyisoprene film products having enhanced tear strength and tensile strength crosslinked with a one polynitrile oxide, intended for direct or indirect contact with living tissue or fluids to be placed in living organisms.

FIELD OF THE INVENTION

This invention relates to thin walled rubber film products, andparticularly those that are made from natural rubber and polyisoprenelatices, vulcanized with polynitrile oxides.

BACKGROUND OF THE INVENTION

Thin walled natural rubber and synthetic polyisoprene film productsintended for medical uses or other contact with human tissue areadvantageously made of vulcanizates with a certain combination ofproperties. In most cases, it is desirable to combine a relatively low100%, 300% or 500% tensile modulus with very high ultimate tensilestrength and ultimate elongation values, and with high tear strengthproperties. Rubber products that may benefit from such enhanced tensileproperties include, for example, medical gloves, condoms, male externalurinary drainage catheters, surgical tubing, contraceptive diaphragms,finger cots, catheter balloons and cuffs, uterine thermal ablationballoons, drug infusion bladders, tissue retrieval pouches, medicaltubing, baby bottle nipples, infant pacifiers, anesthesia breather bags,resuscitation bags, rubber dental dams, exercise bands and surgicaltubing.

With respect to surgical gloves, it is important to have low 100%tensile modulus values, combined with high tensile strength. This is adifficult combination to achieve, as the lower modulus usually producesa lower tensile strength material. A relatively low tensile modulus isnecessary to ensure that such gloves remain comfortable during use. Ifthe tensile modulus is too high, the user's hands may become fatiguedover time as progressively more strength is required to stretch theglove material. This is particularly problematic with gloves that are tobe used for a prolonged period of time such as for a long surgicalprocedure. A combination of low modulus with high tensile strength isnecessary to provide such desired comfort along with a very large safetymargin with respect to glove failure.

Low tensile modulus values are also important in condoms to promote easeof donning, and in catheter balloons where ease of inflation isbeneficial. A low tensile modulus is also of value in elastomeric druginfusion bladders, making it easier to fill the bladder with a drugsolution.

Another tensile property affecting the usefulness of certain thin walledmedical and personal film products is tear strength, important forpreventing premature failure. Baby bottle nipples and baby pacifiersbenefit from high tear strength since this prevents the child's teethfrom severing the nipple or pacifier during use

For catheter balloons, it is very important to combine high tearstrength with high elongation to protect the balloon from burstingduring use. For condoms, the combination of exceptionally high tearstrength and tensile strength combined with high ultimate elongation isvery desirable. For exercise bands, it is desirable to have very highultimate elongation, combined with high tensile strength. Becauseexercise bands are often packed for travel and can impart unpleasantodors to packed clothing, it is very advantageous to have a band withvery low odor.

With respect to rubber dental dams, it is very important to combine veryhigh elongation with very high tensile strength to allow for theplacement of the rubber dam over and around a tooth without risk offailure by tearing. Also it is very desirable for dental dams to havelow levels of odor and taste.

Many rubber products must meet certain standards in order to bemarketed. For example, medical devices, such as surgical gloves,examination gloves and condoms must meet the tensile strength, ultimateelongation and tactility standards of the American Society for Testingand Materials (ASTM). The ASTM has established Standard D3577-88 forrubber surgical gloves, D3578-77 for examination gloves, and D3492-83for condoms. Each of these standards establishes a minimum ultimatetensile strength for the specified product under particular conditions.The minimum ultimate tensile strength specified for Type I (naturallatex) surgical gloves in ASTM D3577-88 is 24 MPa. The minimum ultimatetensile strength specified for Type II (Synthetic rubber latex or rubbercement) surgical gloves in ASTM D3577-88 is 17 MPA. For condoms in ASTMD3492-83, a minimum of 17 MPA is required. The minimum ultimate tensilestrength specified for natural rubber examination gloves in ASTMD3578-00 is 14 MPA. The ASTM standards also establish maximumdeformation stress at 500 percent elongation.

Natural and synthetic rubber have been used extensively as materials forthin walled medical and personal film products. The highest durabilityand flexibility are provided by a rubber film that is seamless and ofuniform thickness. This is best achieved when the thin walled rubberproducts are made by dip-molding and/or casting of the film. Dip-moldingand/or casting of rubber is performed with either a latex (an aqueousdispersion of rubber particles) or an organic solution of the rubber.Dip-molding in either the latex or the organic solution is followed byremoval of the water or solvent; the dipping and water or solventremoval are often performed in repeated cycles to achieve a particularfilm thickness. The film thus formed is then vulcanized to bring therubber to a fully cured state. Latex can be processed without breakingdown the molecular weight of the rubber, whereas dry-rubber methods,which utilize high shear to comminute the rubber and combine it withother compounding ingredients for processing, tend to degrade themolecular weight.

It is generally known that rubbers that are crosslinked only throughcarbon-carbon bonds have inferior tear strengths as compared withrubbers that contain sulfidic and/or polysulfidic crosslinks.Vulcanization, particularly with sulfur, has traditionally beenperformed in the presence of vulcanization accelerators. The most widelyused accelerators are those that contain secondary amino groups, such asdialkylamino groups, cycloalkylamino groups, and morpholinyl groups.Secondary amino groups are found, for example, among the traditionalsulfenamide, dithiocarbamate and thiuram accelerators. An unfortunateconsequence of the inclusion of these accelerators is their tendency toproduce an adverse reaction in individuals with whom the resultingrubber articles may come into contact. The reaction is commonly referredto as a Type IV allergy, which is mediated by T cells, generally occurswithin six to 48 hours of contact with the rubber article, and islocalized in the area of the skin where contact is made. Secondaryamine-containing accelerators are also referred to as nitrosatableamines since they are susceptible of reaction with atmospheric nitrogenoxides during mixing, milling, extrusion, molding, calendaring, curing,and even warehousing and storage, to produce nitrosamines, which havebeen identified as potential human carcinogens.

Typically, sulfur vulcanization in the absence of an accelerator leadsto rubber products with undesirable tensile properties. It would beadvantageous to perform accelerator free vulcanization while achievingoptimal strength of the rubber product thus produced.

Because of the disadvantages of the sulfur vulcanization process, it hasbecome important to develop crosslinking methods that provide usefultensile properties with minimal toxicological properties. Crosslinkingagents that provide rubber vulcanizates 1) free of reaction byproducts,2) without the need for accelerating agents, and 3) through a lowtemperature curing protocol, while maintaining practical physicalproperties would be invaluable.

Polynitrile oxides (PNOs) react readily with unsaturated moleculesbecause they participate in a 1,3-dipolar cycloaddition with a varietyof multiple bond functional groups. In the reaction of a PNO withethylenic points of unsaturation, the cycloaddition product is anisoxazoline ring. Reaction of a rubber compound with a PNO thereforeprovides crosslinking regions within the polymer comprised of two ormore isoxazoline units, usually separated by an aromatic structure.

The high reactivity of PNOs allows for crosslinking to occur at lowertemperatures than with other non-accelerated vulcanization reagents andwithout the formation of byproducts (i.e., virtually all atoms of thereactants are incorporated into the rubber structure). These advantagesof PNO reactivity has cultivated interest in their use as crosslinkingagents for a variety of elastomeric polymers.

For example, the use of polynitrile oxides (PNOs) as low temperaturecrosslinking agents for various types of unsaturated rubber and otherpolymeric materials is known. Breslow, et al. in U.S. Pat. No. 3,390,204disclose the use of various polynitrile oxides to crosslink unsaturatedpolymers. Possible articles of manufacture from such vulcanizates arealso listed, and include items such as tires for motor vehicles, tubing,and pipes. Breslow specifically states that the cross-linked polymersare hard, tough resins. The only physical property disclosed by Breslowis the higher tensile strength of the vulcanizates as compared with thenon-vulcanized starting rubber.

Lysenko, et al. in WO 97/03034 disclose the use of a dispersion ofstable polynitrile oxides useful in latex materials. Specifically, theuse of 2,4,6-triethylbenzene-1,3-dintrile oxide (TON-2) is cited as auseful one part room temperature crosslinking agent for latices. Lysenkoalso notes the utility of TON-2 for crosslinking various polymers tocreate useful one-part coatings. There is no mention of TON-2 or otherpolynitrile oxides imparting any special physical properties to articlesof manufacture. No physical properties of articles or coatings made withTON-2 are disclosed.

Stollmaier, et al. in U.S. Pat. No. 6,753,355 references the utility ofTON-2 for crosslinking various latex polymers for producing foam rubberarticles, including flooring, wall covering, shoe lining, and non-wovenmaterials. Polyisoprene is listed as one of a number of potentiallatices from which foam rubber backings can be made with the use ofTON-2. Only foam containing products are disclosed as articles ofmanufacture.

Parker in U.S. Pat. No. 6,355,826 discloses an improved method ofsynthesizing mesitylene dinitrile oxide (MDNO). Parker cites the use ofMDNO and other polynitrile oxides in the coating of fabrics withrubber-based coatings. Parker states that stable nitrile oxides aredesirable from the perspective of handling, as compared to unstablepolynitrile oxides. The Parker patent contains an extensive list ofreferences to prior uses of MDNO and other polynitrile oxides, which areincorporated herein by reference.

Breton, et al. in U.S. Pat. No. 6,252,009 discloses the use ofpolynitrile oxides for making highly solvent resistant thermoplasticvulcanizates. V. V Boiko and I. V. Grinev, “Influence of MDNO/ProcessingElastomers,” International Polymer Science and Technology, vol. 22, No.7, T/21, 1995 cite the utility of MDNO for increasing the Mooneyviscosity of a synthetic polyisoprene rubber during solid rubber millingoperations.

M. G. Vlasyuk, et al. in “Chemical and toxicological health studies ofelastomer compositions containing dinitrile oxide” International PolymerScience and Technology, 23, No. 7, 1996 discloses the use of fabriccoated with a solvent solution of synthetic polyisoprene vulcanized withMDNO. The toxicological properties of the coated fabric are revealed. Nophysical properties of the coating itself or of the coated fabric areprovided. Latex is not used. Unsupported films are not disclosed.

Russian Patent SU 2,042,664 discloses the physical properties of variouspolymers cured with bis-nitrile oxide. Attention is given to thosepolymers of very low unsaturation, including butyl rubber, urethanerubber, polysiloxane rubber and ethylene propylene rubber. Thesepolymers are generally difficult to crosslink, and MDNO is thought toprovide an advantage to the crosslinking of these polymers, in that MDNOallows for crosslinking with modest time and temperature conditions,including room temperature conditions. Table 1 of this patent shows thattensile strength values were only slightly better for the MDNO curedpolymers than for prior art curing systems. No physical property datawas provided for polyisoprene or natural rubber, as they are highlyunsaturated polymers.

McGlothlin, et al. in U.S. Patent Application 2004/0071909 disclose highperformance rubber vulcanizates from latex for producing thin walledrubber articles. Such vulcanizates contain a combination ofcarbon-carbon bonds, mono and polysulfidic crosslinks, without the useof components that contain secondary amine groups or any nitrosatablesubstances which have a tendency to convert to nitrosamines undercertain conditions. The disclosed vulcanization method offerssignificant advantages over prior art, especially as compared to organicperoxide vulcanized rubber articles of manufacture. However, furtherimprovements in physical properties are still desirable.

McGlothlin et al. in U.S. Pat. No. 6,329,444 disclose the use ofsulfur-free, free-radical-cured cis-1,4-polyisoprene for use indip-molded medical devices. Vulcanizates made by this method are free ofundesirable accelerators and can have very low odor and benon-cytotoxic. However, physical properties of the vulcanizes aregenerally lower than for prior art accelerated sulfur vulcanizates.

McGlothlin, et al. in U.S. Pat. No. 6,775,848 disclose a method ofsecondary vulcanization by imbibing additional vulcanizing agent into analready partially vulcanized article. No disclosure is made to thepossibility of incorporating a vulcanizing agent into a film for primaryvulcanization.

Miller, et al. in U.S. Pat. No. 5,039,750 discloses the addition ofsmall amounts of styrene butadiene latex added to traditional sulfuraccelerated natural rubber latex in an attempt to improve tear strengthand tensile strength properties. Modest improvements in both propertieswere noted. No improvement to odor would be expected, nor is there anynote of the utility to latices which are free of sulfur andvulcanization accelerators.

Anmad in U.S. Pat. No. 5,872,173 discloses the use of silica added tosynthetic latex to improve tear strength.

Amdur et al in U.S. Pat. No. 5,458,588 cites the use of dispersed silicain the prior art sulfur accelerated vulcanizing of natural rubber latexto improve the tensile strength, tear strength, wet strength, breakforce, puncture and tear resistance. While the silica addition appearsto modestly improve both the tensile strength and the tear strength, itdoes so to the detriment of increasing the tensile modulus at lowelongations, and to the detriment of ultimate elongation.

Evans, et. al, “Microencapsulated Antidegradants for Extending RubberLifetime” Rubber Chemistry and Technology Volume 65 No. 1, pp. 201-210discloses the use of microencapsulation technology for extending thelife of rubber compounding agents within compounded dry rubber. Evansalso teaches state of the art technologies involved inmicroencapsulating chemical agents for use in rubber compounds. There isno disclosure in this publication of extending the life of vulcanizationagents within compounded latex.

To the knowledge of the present inventors, there are no prior artpublications which disclose the use of polynitrile oxides as suitablevulcanization agents for thin walled rubber film products made bydip-molding or casting and intended for direct or indirect contact withliving tissue.

Indeed, polynitrile oxides are exceptionally reactive materials,especially with respect to compounds that contain multiple bonds,including the double bonds of rubber materials. This rapid rate ofreaction can result in desirable crosslinking when the polynitrileoxides are used as vulcanizing agents; however it may also lead toextensive pre-vulcanization (i.e., rubber crosslinking that occurs priorto the dipping or casting stage). Although several prior art referencesaddress the use of polynitrile oxides as crosslinking agents for naturalrubber and synthetic cis-1,4-polyisoprene rubber, none of thesereferences teach a method to retard or prevent pre-vulcanization. As faras presently advised, no mention of pre-vulcanization of PNO crosslinkednatural rubber or polyisoprene film products is made in the prior art;however, the methods employed suggest that it would be extensive.

As discussed in SU 2,042,664, cited above, the use of PNOs may be verydesirable for crosslinking rubber materials that have very low levels ofunsaturation. In that case, the high reactivity of the polynitrile oxidecompensates for what would otherwise be a very slow vulcanizationprocess (i.e., with traditional sulfur accelerated cure packages).However, when used to crosslink highly unsaturated materials such asnatural rubber and synthetic polyisoprene, the high rate of reaction ofPNOs makes them more reactive than even the fastest of the “ultraaccelerators” used in sulfur cure systems. At first glance, it wouldappear that polynitrile oxides would be unacceptable crosslinking agentsfor thin walled rubber film products because complete pre-vulcanizationcrosslinking would interfere with the dip-molding or casting process.

Pre-vulcanization of solid rubber materials is a well-known problem.During compounding of dry rubber in rubber mills and the like, heat isgenerated, which can cause some vulcanization to begin. In some cases,this is desirable. In other cases, it is not. For instance, somevulcanization at this stage might improve the green strength of lowmolecular weight rubber materials. During the molding or extruding ofrubber compounds, suitable accelerators are chosen to avoid too muchunwanted early vulcanization of the material (“scorch”) duringprocessing. Rubber compounders select vulcanization accelerators, whichdo prevent the scorch from interfering with the curing process. Withlatex processes, it is permissible to use very rapid accelerators, suchas dithiocarbamates, which would not be suitable for dry rubber. Becauselatex is processed at relatively low temperature, even the so-called“ultra accelerators” can be used, as even these are not too active inrelatively cold latex compounds. For instance, it may take a matter ofdays before a latex compound is ruined due to too much unwantedpre-vulcanization at room temperature.

However, in the case of polynitrile oxide crosslinked rubber filmproducts, if nothing is done to restrict pre-vulcanization, theresulting tensile strength properties of the product films can be about50% of what they otherwise would have been. The reason for this is thattraditional latex compounding practice for making such dip-molded orcast films is virtually always followed by a “maturation” or restingperiod. This maturation period is generally long enough for most of thebubbles to come out of the newly compounded latex but can also allow forextensive pre-vulcanization if methods are not employed for itsprevention. Thus, in the normal course of screening polynitrile oxidesas candidate crosslinking agents for rubber film products, thepolynitrile oxides may well have been eliminated, in the past, fromfurther consideration due to the poor physical properties resulting fromthe extensive pre-vulcanization during maturation.

Accordingly, it is among the objects of the present invention to providethin walled dip-molded or cast rubber film products crosslinked bypolynitrile oxide crosslinking agents, which have been prepared withoutsubstantial pre-vulcanization and which have improved tear strength,ultimate elongation and other properties.

A further object of this invention is to provide a method for formingsuch products.

Other objects and advantages of the products and methods of theinvention will be apparent from the following description of preferredembodiments thereof.

BRIEF SUMMARY OF THE INVENTION

In accordance with the present invention, thin walled, dip-molded orcast rubber film products of a natural rubber or a syntheticpolyisoprene rubber compound, crosslinked with a polynitrile oxidecrosslinking agent are provided having superior physical properties,including improved tear and tensile strengths and ultimate elongation.Preferably, such products have tear strengths from about 15 kN/m toabout 70 kN/m, tensile strength from about 1700 psi to about 6000 psiand ultimate elongation from about 550% to about 1200%.

The method of the present invention for preparing the film productshereof comprises:

-   -   (a) compounding a natural rubber or synthetic polyisoprene        rubber latex so as to substantially reduce or prevent        pre-vulcanization of the resulting rubber compound;    -   (b) dip-molding or casting the rubber compound to form a rubber        film product;    -   (c) admixing the rubber compound or rubber film product with a        polynitrile oxide crosslinking agent; and    -   (d) curing the rubber compound to produce crosslinking thereof.

A preferred method of the present invention for preparing the filmproducts hereof comprises:

-   -   (a) compounding a natural rubber or synthetic        cis-1,4-polyisoprene rubber so as to substantially reduce or        prevent pre-vulcanization of the resulting rubber compound;    -   (b) dip-molding or casting the rubber compound to form a wet or        dry rubber gel;    -   (c) imbibing the polynitrile oxide into the wet or dry rubber        gel; and    -   (d) curing the rubber gel to produce crosslinking thereof.

Pre-vulcanization of the rubber compound is reduced or prevented inaccordance with the present invention by one of a number of alternativetechniques, for example, by reducing the temperature of the rubber latexor its ingredients prior to molding or casting, by microencapsulatingthe polynitrile oxide within a barrier material prior to compounding, orby delaying admixture of the polynitrile oxide with the rubber compoundor film until immediately before curing, or by other techniquesdescribed more fully below.

The present invention thus addresses the need for the production ofnatural rubber and polyisoprene film products that have superior tearstrength, tensile strength and other physical properties. Such products,preferably, meet the published physical property standards required bythe applicable standards for particular rubber film products. While theuse of polynitrile oxides for crosslinking such products has previouslybeen known, we are not aware that they have previously been usedeffectively in producing dip-molded and cast film products. Nor has itbeen known that the use of polynitrile oxide crosslinkers can help toovercome many of the physical property deficiencies of currentlymanufactured medical and personal rubber film products. For example,utilizing the present invention, it is possible to very substantiallyincrease the tear strength of even vulcanizates of accelerator freelatex formulations.

Surprisingly, it has further been discovered that use of the presentinvention facilitates the production of vulcanizates of natural rubberand synthetic polyisoprene which exhibit minimal cell toxicity andexcellent physical property profiles along with low odor and taste.

It has also been discovered in accordance with the present inventionthat the thin walled rubber film products of natural rubber or syntheticpolyisoprene hereof exhibit the noted superior physical properties andyet contain no components that promote nitrosamine formation. Rubberproducts vulcanized with a polynitrile oxide crosslinking agentincorporate an isoxazoline crosslink in the rubber material so as toalleviate the need for secondary amino groups or any other traditionalaccelerators in the rubber compound. When used without suchaccelerators, the present invention can provide rubber products that areoptimal for contact with living tissue due to the elimination of Type IVlatex allergens.

Thin walled rubber film products in accordance with this invention areprimarily contemplated for direct or indirect contact with livingtissue, as well as for direct contact with liquids intended for infusioninto human patients and for contact with gases intended for inhalation.Examples of these articles are medical gloves, condoms, diaphragms,catheter balloons, drug infusion bladders, tissue retrieval pouches,medical tubing, baby bottle nipples, infant pacifiers, anesthesia bags,resuscitation bags, and surgical tubing. Other examples will be apparentto those skilled in medical procedures and the various types ofequipment used in these procedures.

BRIEF DESCRIPTION OF THE DRAWING

The attached FIGURE is a graph illustrating the pot life of filmproducts cured as described in Example 10 below.

DETAILED DESCRIPTION OF THE INVENTION Definitions

As used herein, the term “stable polynitrile oxide” refers to anypolynitrile oxide species that does not readily dimerize or oligomerizeto a polyfuroxan (1,2,5-oxadiazole-2-oxide). Preferably, stablepolynitrile oxides are aromatic structures wherein each polynitrileoxide functionality is flanked with at least one and preferably twoortho groups of the aromatic structure. Ortho groups that provide forstable polynitrile oxides are any ortho groups that are larger than ahydrogen atom and do not themselves react with the polynitrile oxidefunctionality.

Further, the terms “curing” and “vulcanization” are used hereininterchangeably, the term “vulcanization” being used in an analogy withthe vulcanization of natural rubber. Vulcanization is intended to referto the irreversible process during which a rubber compound becomes lessplastic, more resistant to swelling by organic liquids and elasticproperties are conferred, improved, or extended over a greater range oftemperature through change in its chemical structure. In the presentcontext, however, vulcanization is not intended to include crosslinkingwith sulfur or any use of sulfur or sulfur-containing compounds.

The term “pre-vulcanization” is used to refer to vulcanization (e.g.,crosslinking with a polynitrile oxide crosslinking agent) of a rubbercompound prior to making a rubber product. In the context of the presentinvention, pre-vulcanization is any crosslinking that occurs prior tofilm formation through dip-molding or casting techniques.

The term “compound” refers to the mixture of rubber and additives fromwhich the rubber product is made.

The term “maturation” refers to a period of time after the formation ofa latex compound in which the latex compound is stored prior toprocessing. Maturation is typically a period of time wherein thecolloidal properties of the latex have changed.

The term “accelerator” refers to a compounding material used in smallamounts with a vulcanizing agent to increase the speed of vulcanizationand enhance the physical properties of the vulcanizate.

The term “nitrosatable” refers to any substance susceptible of reactionwith atmospheric nitrogen oxides during mixing, milling, extrusion,molding, calendaring, curing, and even warehousing and storage, toproduce nitrosamines.

The term “gel” refers to a colloidal rubber compound set into a jelly.Gels are formed through the process of gelation which converts therubber compound to a gel of the same external shape as the vessel ormold in which it is placed.

The term “former” refers to an article having the same shape of thefinished product, e.g., a mandrel. A former is immersed into the rubbercompound during the dip-molding process.

The term “crosslinking” is intended to refer to the process of bridgingindividual rubber molecules through the formation of covalent chemicalbonds between the rubber molecules. In the context of crosslinking witha polynitrile oxide, rubber molecules are bridged together with astructure containing at least two isoxazoline units.

The term “low temperature curing” refers to a curing process in whichall steps of the process are carried out at a temperature of about 150°F. or less.

The term “aryl” refers to an conjugated unsaturated carbocyclic grouphaving 6-21 carbon atoms and having a single ring such as phenyl ormultiple fused rings such as naphthyl or anthracyl. Suitable examplesinclude, but are not limited to, phenyl, naphthyl, biphenyl,dibenzofuranyl, and dibenzothiophenyl. The aromatic structure mayoptionally be further fused to an aliphatic or another aromaticstructure or can be substituted with one or more substituents such ashalogen (fluorine, chlorine and/or bromine), hydroxy, thio, C₁-C₇ alkyl,C₁-C₇ alkoxy or aryloxy, C₁-C₇ alkylthio or arylthio, C₁-C₇alkylsulfonyl or alkylsulfoxy, or any other group that is not reactivewith a nitrile oxide functionality. In the context of the presentinvention, when the aromatic structure contains more than one aromaticring (e.g., fused aromatic rings, aromatic rings directly bonded to oneanother, or aromatic rings connected through another functionality), thenitrile oxide functionalities may be bonded to one or more of thearomatic rings.

The term “bulky group”, in the context of the present invention, refersto an organic functional group that is larger than a hydrogen atom andis not reactive with a nitrile oxide functionality. Suitable examplesinclude, but are not limited to halogen (fluorine, chlorine and/orbromine), hydroxy, thio, C₁-C₇ alkyl, C₁-C₇ alkoxy or aryloxy, C₁-C₇alkylthio or arylthio, C₁-C₇ alkylsulfonyl or alkylsulfoxy.

As indicated above, one aspect of the present invention comprises thinwalled, dip-molded or cast rubber film products made from a naturalrubber or a synthetic polyisoprene rubber compound and crosslinked witha polynitrile oxide crosslinking agent.

In such products, the polynitrile oxide fully reacts with the polymersand becomes part of the crosslinked thin walled film product. As notedabove, film products that are cured with polynitrile oxide crosslinkingagents contain rubber molecules that are bridged together with astructure containing at least two isoxazoline units.

The thin walled, dip-molded or cast rubber film products hereofincorporate the structure shown in formula (I);

wherein

A represents an aryl group substituted by a bulky group in at least oneortho position to the isoxazoline rings, wherein the aromatic structurehas a ratio of hydrogen atoms to carbon atoms of less than 1:1 andwherein the bulky group is substantially unreactive with a nitrile oxidefunctionality.

-   -   R¹ represents the natural rubber or cis-1,4-polyisoprene rubber        polymer chain associated with the material;    -   R² and R³ are independently selected from hydrogen and methyl        wherein;    -   When R² is methyl, R³ is hydrogen and,    -   When R³ is methyl, R² is hydrogen.

In a preferred embodiment of the present invention, the thin walled,dip-molded or cast rubber film products are crosslinked with stablepolynitrile oxides such as MDNO or TON-2 and incorporate the structureshown in formula (II)

-   -   wherein,    -   R¹ represents the natural rubber or cis-1,4-polyisoprene rubber        polymer chain associated with the material;    -   R² and R³ are independently selected from hydrogen and methyl        wherein;    -   When R² is methyl, R³ is hydrogen and,    -   When R³ is methyl, R² is hydrogen.    -   R⁴ is methyl or ethyl.

Even if the polynitrile oxide were not to fully react during themanufacturing process, i.e., upon curing, it would likely fully react atroom temperature shortly thereafter. This is very significant from theperspective of medical and personal film products, which directly orindirectly contact human tissue. Most vulcanization systems, with thepossible exception of high-energy radiation crosslinking, involve therelease of reaction byproducts. This is especially true of sulfuraccelerated vulcanization systems wherein the traditionalnitrogen-containing accelerators can lead to nitrosamine formation andultimately to Type IV allergic reactions when the rubber products comeinto contact with living tissue. It is also true of organic peroxidecure systems. Although the byproducts of peroxide vulcanization aregenerally not toxic, they may be objectionable with respect to odor andtaste created by the breakdown products of the organic peroxide(s). Forinstance, in the case of dicumyl peroxide, odorous acetophenone isreleased as a breakdown product. While high energy radiation freeradical vulcanization may not release residuals, typically some type ofradiation sensitizer is used, which produces an undesirable odor.

As a result of polynitrile oxide crosslinking, no residual chemicalswould remain in the fully cured rubber compound. The production ofrubber film products using this method therefore, possess nonitrosatable substances and Type IV allergens and a very low odor andtaste.

The thin walled film products of the present invention have:

-   -   a tear strength from about 15 kN/m to about 70 kN/m; preferably        from about 25 kN/m to about 60 kN/m; and more preferably from        about 40 kN/m to about 60 kN/m;    -   an ultimate tensile strength from about 1700 psi to about 6000        psi; preferably from about 2450 psi to about 5500 psi; more        preferably from about 3300 psi to about 4500 psi;    -   a 100% tensile modulus from about 70 psi to about 130 psi;        preferably from about 80 psi to about 120 psi; more preferably        from about 90 psi to about 110 psi;    -   a 300% tensile modulus from about 140 psi to about 280 psi;        preferably from about 160 psi to about 260 psi; more preferably        from about 180 psi to about 220 psi;    -   a 500% tensile modulus from about 200 psi to about 1200 psi;        preferably from about 300 psi to about 800 psi; more preferably        from about 350 psi to about 500 psi; and    -   an ultimate percent elongation from about 550% to about 1200%;        preferably from about 700% to about 1100%; more preferably from        about 800% to about 1050%.

Natural rubber utilized in the products hereof can be obtained fromseveral sources, including Hevea brasiliensis, Parthenum argentatum(commonly known as “guayule”), and Ficus elastica rubber trees. Methodsfor obtaining natural rubber latices from non-Hevea sources, such as theLactrius Volemus mushroom and the Russian dandelion are described inU.S. Pat. No. 5,580,942, issued Dec. 3, 1996, to Cornish. Natural rubberlatex is available in several grades, including high ammonia latex, lowammonia latex, and others. All such varieties are suitable for use inthe products and methods of the present invention. The invention alsoextends to natural rubber latices that have been processed to reduce theamount of proteins present in the latices. Some of these processesinclude centrifuging to separate and remove water, and others includedouble centrifuging, in which an initial centrifuging is followed by theaddition of water and a second centrifuging. Still other processesinvolve the use of enzymes to digest the proteins. Descriptions ofapplicable enzyme methods are found in U.S. Pat. No. 5,610,212 Mar. 11,1997, U.S. Pat. No. 5,569,740, Oct. 29, 1996, and U.S. Pat. No.5,585,459, Dec. 17, 1996, all to Tanaka et al. An example of acommercially available deproteinized rubber latex which may be utilizedin the present invention is ALLOTEX®, obtainable from TillotsonHealthcare Corporation, Rochester, N.H., USA.

Synthetic cis-1,4-polyisoprene useful herein is commercially availablein the United States from The Goodyear Tire & Rubber Company, Beaumont,Tex., USA., in Western Europe from Kraton Polymers Division ofRipplewood Holdings LLC, Bemis, Netherlands, and in Japan from JapanSynthetic Rubber Co., Ltd., and from Nippon Co., Ltd. Such polymer isproduced by polymerizing isoprene over a Ziegler catalyst consisting ofisobutylaluminum and titanium tetrachloride, or alkali metal catalystssuch as finely divided lithium metal or organolithium compounds. Othercatalysts known in the polyisoprene art can be used as well. The polymeris also capable of preparation by processes involving anionicpolymerization, cationic polymerization, and free-radicalpolymerization. These processes, and the conditions under which they areperformed are known in the art. For typical syntheticcis-1,4-polyisoprene prior to crosslinking, the weight-average molecularweight generally ranges from about 750,000 amu to about 950,000 amu, andthe number-average molecular weight generally ranges from about 250,000amu to about 350,000 amu. Synthetic cis-1,4 polyisoprene prepared by theZiegler catalyst route has about 96 to about 98% of its monomeric unitsjoined in cis-1,4 orientation. In those made via anionic polymerization,about 90% to about 92% of the monomeric units are joined in cis-1,4orientation. Preferred synthetic cis-1,4-polyisoprenes for use in thisinvention are those produced either by the aforesaid Ziegler catalysisor anionic polymerization methods.

In a preferred embodiment of the present invention, the natural rubberor cis-1,4-polyisoprene rubber is in the form of a latex. Latices ofnatural rubber or cis-1,4-polyisoprene are formed by methods known tothose skilled in the art of rubber compounding and processing. Thesemethods include either emulsification of an organic solution of thepolymer in an aqueous medium followed by removing the solvent, orliquefaction of the polymer and combining the liquefied polymer with theaqueous medium under emulsification conditions. The emulsion can bestabilized by various emulsifying agents. Typical emulsifying agentswhich may be so utilized are potassium and sodium salts of rosin acidsand higher fatty acids, such as potassium and sodium salts of oleicacid, palmitic acid, stearic acid, lauric acid, myristic acid, arachidicacid, and ricinic acid, as well as sulfates and sulfonates of theseacids, such as sodium lauryl sulfate and sodium lauryl sulfonate. Othersuitable emulsifying agents are amine salts of hydroxylamines oflong-chain fatty acid esters, quaternary ammonium salts such asstearyldimethylbenzylammonium chloride andtridecylbenzenehydroxyethylimidazole chloride, phosphoric esters ofhigher alcohols such as capryl and octyl alcohol, and monoesters ofoleic acid and pentaerythritol such as sorbitan monooleates. Therelative amounts of each phase may vary, although in most cases, thevolume ratio (organic:aqueous) will range from about 0.5:1 to about20:1, and preferably from about 0.75:1 to about 1.25:1, for bestresults. When an organic solvent is used, suitable solvents arealiphatic hydrocarbons, preferably those containing 5 to 8 carbon atoms,e.g., pentane, pentene, hexane, heptane, cyclohexane, cyclopentane, andtetrahydrofuran. The solvent is readily removed by evaporation or otherconventional means to leave the solvent-free aqueous latex. If desired,the latex can then be concentrated by conventional methods, one exampleof which is ultrafiltration as disclosed by DelPico, U.S. Pat. No.4,160,726 (Jul. 10, 1979) and by Tanaka et al., U.S. Pat. No. 5,569,740(Oct. 29, 1996).

Polynitrile oxide crosslinking agents suitable in the practice of thepresent invention are any polynitrile oxides that bond the individualrubber molecules of the thin walled film products with at least twoisoxazoline moieties within each crosslink unit. PNO crosslinking agentsmay be any of the PNO crosslinking agents known in the prior art, forexample those appearing in U.S. Pat. No. 3,390,204, U.S. Pat. No.6,252,009, and U.S. Pat. No. 6,355,826. The PNOs used in the practice ofthe present invention may be added neat, or in an aqueous or organicdispersion, and may be present as mixtures of more than one PNO. It ispreferred that the polynitrile oxides used in the practice of thepresent invention are stable polynitrile oxides. Examples of specificstable PNOs for the practice of the present invention include thefollowing compounds:

Preferably, the PNO is mesitylene dinitrile oxide (MDNO) or2,4,6-triethylbenzene dinitrile oxide (TON-2)

The organic solvent which is used either in forming the latex or as thesolvent when an organic solution rather than a latex is used as adipping medium, can be any solvent that is inert to the polyisoprene andis readily removable by evaporation from the dip-molded film. Thesolvent is preferably an aliphatic hydrocarbon, saturated orunsaturated, linear, branched, or cyclic; or ethers, esters, alcohols,or amines. Typical solvents are aliphatic hydrocarbons containing 5 to 8carbon atoms, such as pentane, pentene, hexane, heptane, cyclohexane andcyclopentane, and tetrahydrofuran.

Antioxidants, antiozonants, and other additives may be utilized in thefilm products of the invention. Antioxidants and antiozonants may beincluded to protect against environmental aging. Preferred antioxidantsare hindered phenolic compounds, e.g.,4-{[4,6-bis(octylthio)-s-triazin-2-yl]amino}-2,6-di-t-butyl-phenol,2,4-bis[(octylthio)methyl]-o-cresol, and polymerized1,2-dihydro-2,2,4-trimethylquinoline.

Small amounts of other rubber materials can also be included asadditives or blending agents. The use of carboxylated styrene butadienerubber with at least 50% styrene content is preferred as a reactivereinforcing agent. Other reinforcing agents may also be included in someembodiments of the invention. Examples of suitable reinforcing agentsare silica (notably fumed silica), carbon black, and chopped fibers. Theuse of fibers to improve the tear strength of medical gloves isdisclosed in U.S. Pat. No. 6,021,524, issued Feb. 8, 2000, to Wu et al.,and the use of fumed silica to improve the tear strength of dipped filmsis disclosed in U.S. Pat. No. 5,872,173, issued Feb. 16, 1999, to Anand.Pigments and dyes may also be included, as may any of the otheradditives known to those skilled in the art of rubber formulations andthe manufacture of rubber products.

The rubber compounds used in the present invention may further include asufficient amount of a surfactant, depending on the end productapplication, to act as a mechanical and chemical stabilizer in thesynthetic latex system. The particular type of surfactant used will varydepending on the colloidal system of the latex itself. For example,anionic surfactants such as salts of alcohol sulfates are known to beuseful as mechanical stabilizers and wetting agents in many anioniclatexes. Cationic latices, on the hand, typically require cationic ornon-ionic surfactants such as quaternary ammonium salts. In oneembodiment of the present invention, the rubber may be compounded with asufficient amount of an anionic surfactant, such as DARVAN® WAQ (sodiumalkyl sulfate) or DARVAN® SMO surfactant (DARVAN is a registeredtrademark of Vanderbilt Company, R. T., Inc.). Preferably, thesurfactant is in an amount ranging between about 0.2 phr to about 2.0phr.

Additionally, the rubber compound used in the present invention may betreated with a coagulant prior to curing. Coagulants are used to helpthe latex adhere to the former in the dip-molding operation by forcingthe latex particles to form a hydrated film (i.e., wet gel) on thesurface of the former. Typically, a coagulant is dissolved in water andset up in a separate dipping bath. The former is first immersed into theliquid coagulant bath to coat the former with coagulant solution. Someor all of the carrier water is then evaporated from the former, leavinga very thin layer of coagulant on the surface of the former. Thecoagulant coated former is then immersed into the compounded latex bathwhere the coagulant destabilizes the latex particles to form a wet gel.Conventional coagulants used in the rubber industry can be used,including salts, polyvalent cations such as calcium nitrate, mixtures ofcalcium nitrate and calcium chloride, acids (including volatile acidssuch as acetic and formic acid), and dehydrating solvents. A preferredcoagulant is calcium nitrate. In one embodiment of the presentinvention, the coagulant solution contains an additional surfactant,preferably Igepal CO-630, to allow for proper wetting of the coagulantsolution onto the surface of the former.

The various components of the latex can be combined in any manner thatwill produce a fluid medium with uniformly dispersed solids or droplets.Preferably, the individual components are first placed in fluid form,either as solutions or aqueous-based emulsions or dispersions. In thepreferred compounding technique, the individual fluids are then combinedby simple mixing to form the latex.

If one wishes to concentrate the latex by reducing the amount of waterin the latex before dip-molding, water can be removed from the latex byconventional methods. A preferred method is ultrafiltration.Ultrafiltration membranes and their use in concentrating latices aredisclosed by DelPico, U.S. Pat. No. 4,160,726 (Jul. 10, 1979) and Tanakaet al., U.S. Pat. No. 5,569,740 (Oct. 29, 1996).

Although the final film thickness is not critical in this invention,preferred films are those whose thickness is about 0.02 inch (0.051 cm)or less, most preferably from about 0.001 inch (0.0025 cm) to about 0.02inch (0.051 cm). For surgical gloves, a particularly preferred thicknessrange is from about 0.003 inch to about 0.015 inch (about 0.0076 cm toabout 0.038 cm). For condoms, a particularly preferred thickness rangeis from about 0.002 inch to about 0.005 inch (about 0.005 cm to about0.013 cm). Other products, such as catheter balloons, may have differentranges that are particularly preferred, but all will be within thebroader ranges cited above, and all will be readily apparent to thoseskilled in the manufacture of such products.

In accordance with the method aspect of the present invention, the veryhigh level of reactivity of the polynitrile oxides should be taken intoaccount to prevent premature reaction of the polynitrile oxide with therubber compound, i.e., prior to the formation of a wet or dry gel of therubber article. This will prevent the rubber compound from excessivepre-vulcanizing (pre-curing). The inhibition of pre-vulcanization can bedone in a number of different ways.

In a first embodiment, the temperature of the compounding ingredientsmay be significantly reduced prior to mixing (e.g., from a temperaturefrom about 32° F. to 75° F.), and the compounded latex may then bestored at a reduced temperature (e.g., from a temperature from about 32°F. to 60° F.) prior to use. This technique is useful, but it only slowsdown the pre-vulcanization process to an extent. For rubber compoundsthat can be used within 60 minutes or less, preferably 30 minutes orless, and most preferably 15 minutes or less from the time thepolynitrile oxide is added to the rubber compound, this can be a veryuseful technique. For instance, this technique is useful in the castingof rubber sheeting for use in rubber dental dams can be producedeffectively in this manner.

In an alternative preferred embodiment, the polynitrile oxide orpolynitrile oxide dispersion may be microencapsulated within a barriermaterial coating prior to compounding it into the rubber mixture. Thepolynitrile oxide is thus prevented from reacting with significantnumbers of rubber particles until the outer shell of the microcapsulesare breached, thus allowing the polynitrile oxide to begin thecrosslinking reaction. By way of example only, the heating of the wet ordry gel of the rubber compound (e.g., from a temperature from about 80°F. to 212° F.) can breach the outer shell of a suitablemicroencapsulated particle, thus allowing the vulcanization reaction tobegin. This microencapsulation technique is very well suited when alarge volume of compounded rubber is to be prepared in advance of itsuse to produce dip-molded or cast articles. This is especially useful indip-molding processes, where dip tanks hold much compounded rubber, andthe residence time of the rubber is long, due to the relatively smallamount of compound removed by each dipping former.

In still another alternative embodiment, the rubber is compounded withall ingredients, except for the polynitrile oxide dispersion.Immediately prior to use, the polynitrile oxide can then be added. In acontinuous system, the polynitrile oxide can be mixed in with a meteringpump, for instance. Alternatively, the polynitrile oxide can be mixeddirectly into a small batch of otherwise fully compounded rubber,immediately prior to use. In the case of cast films for rubber sheetingfor producing dental dams and the like, this works exceptionally well.Once mixed, the polynitrile oxide is free to react, but the full volumeof compounded rubber is almost immediately used up in the manufacturingprocess.

Additionally, pre-vulcanization may be substantially reduced oreliminated by forming a wet or dry gel of the rubber compound, whichdoes not contain a polynitrile oxide, and then imbibing the polynitrileoxide into the film. Once imbibed, the vulcanization reactionimmediately begins, and forms a fully post-vulcanized vulcanizate withexcellent properties. A suitable solvent needs to be chosen, such astoluene, or an alkyl acetate, which can dissolve the polynitrile oxideand preferably only swells the rubber gel. Such technique works verywell for relatively small items, such as catheter balloons.

In yet another embodiment to substantially reduce or eliminatepre-vulcanization, the polynitrile oxides are placed in a coagulationbath. Polynitrile oxide is thus kept away from the rubber compound,until the rubber is actually being processed. This method works bestwith thin films, especially those films with wall thicknesses of 0.005″or less.

In a further embodiment, a dip-molding or casting operation may beperformed which lays down alternating layers of rubber compound andpolynitrile oxide dispersion or polynitrile oxide dissolved in solvent.This technique overcomes the film thickness limitations of the priormethod, but does add some complexity.

Additionally, pre-vulcanization may be substantially reduced oreliminated by the constant addition of new, freshly made compoundedrubber to a dip tank of relatively small internal volume, and thenprocessing a very large number of formers very quickly. In this manner,the resonance time for the compounded rubber is very short, allowing foronly a small amount of pre-vulcanization.

In yet another alternative embodiment, pre-vulcanization may besubstantially reduced or eliminated by substantial reduction orelimination of a maturation period for the compounded rubber. By way ofexample only, the maturation period of the rubber compound prior to filmformation is from about 0 hours to about 48 hours, preferably, fromabout 0 hours to about 24 hours.

As indicated above, the present invention involves the formation of thinfilms with dip-molding or casting techniques; however, formation of alatex into a thin film can be accomplished by any conventional method,including spraying, rolling, the use of a doctor blade, or variousmolding techniques well known in the art. For many medical and personaldevices, particularly those that are hollow, such as condoms, surgicaland examination gloves, and finger cots, dip-molding is an especiallyeffective and convenient means of forming the film. The film may or maynot be self supporting, depending on the application. Dip-molding isachieved by dipping a mandrel, or in general terms, a form whose outersurface has the configuration of the product to be formed, in a liquidmedium that contains the liquefied polymer, then withdrawing the formfrom the liquid to leave a continuous film of the liquid over thesurface of the form. The liquid medium may be either a latex (an aqueousemulsion of the polymer in which the polymer is the dispersed phase andwater or an aqueous solution is the continuous phase) or a solution ofthe polymer in an organic solvent. The film is then dried in place onthe form (i.e., the solvent or carrier liquid is evaporated) and thepolymer is cured (vulcanized) either before or after the drying step.The dried and cured film, which is now the product in its final shapeand composition, is then stripped from the form.

The technique used for curing in the present invention can be anytechnique for obtaining complete crosslinking of the polynitrile oxidecrosslinking agent with the rubber compound. Curing can take place in aconvection oven, forced convection oven, steam chamber, or molten mediabath. Additionally, infrared heating or microwave heating techniques maybe used, or the film product can remain at room temperature until curingis completed. Thin walled dip-molded or cast rubber film products can becured at temperatures ranging from about 0° F. to about 350° F. In apreferred embodiment of the present invention, film products are curedat a temperature from about 60° F. to about 212° F.

It is often useful to determine the extent to which a dipped film orarticle has been vulcanized. A commonly used method is to cut out acircular disk of the cured film and measure the change in diameter uponimmersion of the disk in a solvent bath. A detailed explanation of thistest and its use with polyisoprene latex is found in U.S. Pat. No.3,215,649, issued Nov. 2, 1965, to Preiss et al., entitled “SyntheticLatex.” Similar test methods are available for other types of vulcanizedpolymers, and are well known to those skilled in the art.

The following examples are given for purposes of illustration and arenot intended to limit the scope of the invention. All test films in theexamples were prepared by the following technique unless otherwiseindicated.

Test Films

Materials:

(1) Latices

Synthetic cis-1,4-polyisoprene latex containing approximately 60%solids, Product No. IR-RP401, supplied by Kraton Polymers.

Natural Rubber Latex (NRL) Centex HF containing 61.3% solids, suppliedby Centro Trade Rubber USA, Inc., Virginia Beach, Va.

(2) Crosslinking Agents

Mesitylene Dinitrile Oxide (MDNO) Dispersion, prepared by Apex MedicalTechnologies, Inc. The following procedure was used to prepare anaqueous dispersion of 30% active MDNO for easy addition of MDNO into alatex system. A 60 ml polypropylene bottle is filled about half fullwith ¼″ diameter steel spheres. These spheres will serve as the grindingmedia for dispersing the MDNO. Solid MDNO, Darvan #1 dispersing agent,Van Gel B viscosity stabilizer, Igepal CO-630 surfactant and water arethen added to the bottle. The bottle was closed and then rolled on alaboratory roll mill for up to 3 hours until the MDNO was fullydispersed.

Dicumyl Peroxide Dispersion: A master batch of 37% solids dicumylperoxide dispersion was prepared by mixing the following materials fortwo minutes under high shear: 100 g of dicumyl peroxide, 66.5 g oftoluene, 5.6 g of oleic acid, 101 g of deionized water, and 2.6 g of 30weight percent aqueous potassium hydroxide solution. This resulted in adispersion in which the dicumyl peroxide was uniformly dispersed.

Sulfur Dispersion: The sulfur was a 68% active sulfur dispersioncommercially available as Bostex 410, supplied by Akron Dispersions,Akron, Ohio, USA. A zinc oxide dispersion was also used, consisting of62% active zinc oxide commercially available as Octocure 462, suppliedby Tiarco Division of Textile Rubber and Chemical Co., Inc., Dalton,Ga., USA.

(3) Surfactant

Darvan WAQ (Sodium Alkyl Sulfate), 30% TSC, supplied by R. T. VanderbiltCompany, Inc., Norwalk, Conn.

(4) Reinforcing Agent

Styrene Butadiene Rubber Latex (SBR), prepared by Apex MedicalTechnologies, Inc., San Diego, Calif. The styrene-butadiene rubber latexused for compounding is a mixture of Rovene 4106 and Rovene 4457. Thetwo styrene-butadiene rubber latexes are added to a plastic jug androlled on a laboratory roll mill for a few minutes creating a blend thathas a total styrene content of 77% and a total percent solid content of52.4%. Rovine is the trademark of Mallard Creek Polymers, Charlotte,N.C. 28262.

Cab-O-Sperse GP-50 water-dispersed fumed silica. The silica was a 20%(by weight) aqueous dispersion, supplied by Cabot Corporation

(5) Antioxidant

The antioxidant consisted of a dispersion of Irganox 565(4-[[4,6-Bis(octylthio)-s-trianzin-2-yl]amino]-2,6-di-butylphenol),supplied by Ciba Chemicals.

(6) Coagulant Solution

The coagulant solution consisted of a mixture of 3,975 grams ofdeionized water, 1,000 calcium nitrate and 25 g of Igepal CO-630surfactant. All ingredients were mixed together until dissolved, andthen the solution was allowed to age 3 days prior to use. Igepal CO-630(Nonyl Phenol 9 Mole Ethoxylate) was supplied by Stepan Company,Northfield, Ill. USA.

Preparation of Test Films:

Ingredients for each of the following formulations were weighed into a500 mL polyethylene bottle and mixed under medium shear (30 RPM) for 15minutes at room temperature using a laboratory XP mixer, then rolled for15 minutes on a laboratory roll mill. The formulation was filtered intoa polyethylene graduated cylinder and degassed for a period of 10minutes at a vacuum level of 15 inches Hg.

The respective test films were dip-molded on 32 mm glass mandrelswithout a maturation period for the compounded latex. The mandrels werepre-heated in a 150° F. oven, then dipped into the coagulant solution ata speed of 0.8 inches per second and lifted out at a speed of 0.2 inchesper second. The mandrels were allowed to dwell in the coagulant for 15seconds. The coagulant coated mandrels were dried for 5 minutes in a150° F. oven. The mandrels were thereafter dipped into the latex at aspeed of 0.8 inches per second and lifted out at an exit speed of 0.2inches per second. The mandrels were allowed to dwell in the latex for15 seconds.

Once dipped, the films were dried for 5 minutes in a 150° F. oven. Thefilms were leached in a 60° C. water bath for 3 minutes. The resultingfilms were then dried in a 150° F. oven for 60 minutes. The peroxidecured films were additionally cured for 9 minutes in a 350° F. saltbath.

The films were rinsed, stripped with powder and readied for tear testingper ASTM D624, and for tensile testing per ASTM D3492.

The test films prepared in the following examples and comparativepreparations were formed by dip-molding as described above.

Comparison of Synthetic Polyisoprene Films Crosslinked with MDNO(Examples 1-4) with Synthetic Polyisoprene films Crosslinked withDicumyl Peroxide (Comparative Preparations A-D)

EXAMPLE 1 Comparative Preparation A Comparison of Polyisoprene LaticesPlus an SBR Reinforcing Agent Cured with MDNO (Example 1) and DicumylPeroxide (Comp. Prep. A) Crosslinking Agents

TABLE 1 MDNO and Peroxide-Cured Polyisoprene Films with SBR ReinforcingAgent Example 1 Comp. Prep. A Parts by Parts by Weight Weight Ingredient% TSC^(a) (Dry) % TSC (Dry) Synthetic Polyisoprene Latex 60 100 60 100(SPIL) IR-307 Styrene Butadiene Rubber Latex 52.4 5 52.4 5 (SBR) MDNODispersion 30 1.2 — — Dicumyl Peroxide Emulsion — — 37 1.2 Darvan WAQsurfactant 30 0.5 30 0.5 Cab-O-Sperse GP-50 Aqueous 20 2 20 2 SilicaDispersion Antioxidant Dispersion 50 2 50 2 Deionized Water - asnecessary to dilute compound to 45% TSC ^(a)% TSC is Total SolidsContent of Each Respective Ingredient

Determination of Tensile Properties

The dip-molded thin films prepared from the formulations of Example 1and Comp. Prep. A were subjected to mechanical tests to determine theirtensile properties. Values for 50%, 100%, 300%, and 500% tensile moduluswere measured as well as values for ultimate tensile strength, ultimateelongation and tear strength. The physical property testing wasperformed in accordance with the ASTM D-3492 standard for condom rings.

TABLE 2 Comparison of Tensile Properties of MDNO and Peroxide Cured SBRReinforced Polyisoprene Films Property Example 1 Comp. Prep. A TensileModulus  50% 66 58 100% 91 92 300% 164 199 500% 257 396 Ultimate TensileStrength 4911 3402 (psi) Increase in Tensile Strength 44.36% — (Ex. 1 vsComp. Prep. A) Ultimate Percent 1124 801 Elongation (%) Tear Strength(kN/m) 36.2 12.7 Increase in Tear Strength   185% — (Ex. 1 vs Comp.Prep. A)

As will be apparent from the preceding tabulation, Example 1 (utilizingMDNO as the crosslinking agent with a conventional SBR reinforcing agentbut free of accelerator) exhibits superior tensile and tear propertiesas compared with Comp. Prep. A. (utilizing a peroxide crosslinkingagent, but otherwise identical). Moreover, notwithstanding the increaseof tensile and tear properties, the tensile modulus values remained low.

EXAMPLE 2 Comparative Preparation B Comparison of Polyisoprene LaticesCured with MDNO (Example 2) and Dicumyl Peroxide (Comp. Prep. B)Crosslinking Agents

TABLE 3 MDNO and Peroxide-Cured Polyisoprene Films (with SBR omitted)Example 2 Comp. Prep. B Parts by Parts by Weight Weight Ingredient % TSC(Dry) % TSC (Dry) Synthetic Polyisoprene Latex 60 100 60 100 (SPIL)IR-307 MDNO Dispersion 30 1.2 — — Dicumyl Peroxide Emulsion — — 37 1.2Darvan WAQ surfactant 30 0.5 30 0.5 Cab-O-Sperse GP-50 Aqueous 20 2 20 2Silica Dispersion Antioxidant Dispersion 50 2 50 2 Deionized Water - asnecessary to dilute compound to 45% TSC

TABLE 4 Comparison of Tensile Properties of MDNO and Peroxide CuredPolyisoprene Films Property Example 3 Comp. Prep. B Tensile Modulus  50%56 48 100% 84 77 300% 152 165 500% 238 335 Ultimate Tensile Strength4912 3337 (psi) Increase in Tensile Strength 47.2% — (Ex. 2 vs Comp.Prep. B) Ultimate Percent 1105 791 Elongation (%) Tear Strength (kN/m)33.2 11.2 Increase in Tear Strength  196% — (Ex. 2 vs Comp. Prep. B)

As will be apparent from the preceding tabulation, Example 2 (utilizingMDNO as the crosslinking agent) exhibits superior tensile and tearproperties as compared with Comp. Prep. B. (utilizing a peroxidecrosslinking agent, but otherwise identical), even with the SBRreinforcing agent omitted. These experiments show the limitedcontribution that the SBR makes to increased tear strength, while theMDNO crosslinker significantly increases the tensile strength and tearstrength.

EXAMPLE 3 Comparative Preparation C Comparison of Polyisoprene LaticesPlus an SBR Reinforcing Agent, Cured with MDNO/Sulfur (Example 3) andDicumyl Peroxide/Sulfur (Comp. Prep. C) Crosslinking Agents

TABLE 5 MDNO and Peroxide-Cured Polyisoprene Films (with sulfur) Example2 Comp. Prep. B Parts by Parts by Weight Weight Ingredient % TSC (Dry) %TSC (Dry) Synthetic Polyisoprene Latex 60 100 60 100 (SPIL) IR-307Styrene Butadiene Rubber Latex 52.4 5 52.4 5 (SBR) Sulfur Dispersion 680.4 68 0.4 MDNO Dispersion 30 1.2 — — Dicumyl Peroxide Emulsion — — 371.2 Darvan WAQ surfactant 30 0.5 30 0.5 Cab-O-Sperse GP-50 Aqueous 20 220 2 Silica Dispersion Antioxidant Dispersion 50 2 50 2 DeionizedWater - as necessary to dilute compound to 45% TSC

TABLE 6 Comparison of Tensile Properties of MDNO and Peroxide CuredPolyisoprene Films (with sulfur) Property Example 3 Comp. Prep. CTensile Modulus  50% 65 55 100% 96 80 300% 176 150 500% 291 245 UltimateTensile Strength 4666 4361 (psi) Increase in Tensile Strength 7.0% —(Ex. 3 vs Comp. Prep. C) Ultimate Percent 1081 1084 Elongation (%) TearStrength (kN/m) 39.6 18.1 Increase in Tear Strength 118.8% — (Ex. 3 vsComp. Prep. C)

As will be apparent from the preceding tabulation, Example 3 (utilizingMDNO and sulfur as the crosslinking agents with a conventional SBRreinforcing agent but free of accelerator) exhibits modestly highertensile and substantially higher tear strength as compared with Comp.Prep. C. (utilizing peroxide and sulfur as crosslinking agents, butotherwise identical). Moreover, notwithstanding the increase of tensileand tear properties, the tensile modulus values remained low.

EXAMPLE 4 Comparative Preparation D Comparison of Polyisoprene LaticesCured with MDNO/Sulfur (Example 4) and Dicumyl Peroxide/Sulfur (Comp.Prep. D) Crosslinking Agents

TABLE 7 MDNO/Sulfur and Peroxide/Sulfur Cured Polyisoprene Films Example4 Comp. Prep. D Parts by Parts by Weight Weight Ingredient % TSC (Dry) %TSC (Dry) Synthetic Polyisoprene Latex 60 100 60 100 (SPIL) IR-307Sulfur Dispersion 68 0.4 68 0.4 MDNO Dispersion 30 1.2 — — DicumylPeroxide Emulsion — — 37 1.2 Darvan WAQ surfactant 30 0.5 30 0.5Cab-O-Sperse GP-50 Aqueous 20 2 20 2 Silica Dispersion AntioxidantDispersion 50 2 50 2 Deionized Water - as necessary to dilute compoundto 45% TSC

TABLE 8 Comparison of Tensile Properties of MDNO/Sulfur andPeroxide/Sulfur Cured Polyisoprene Films (SBR Absent) Property Example 4Comp. Prep. D Tensile Modulus  50% 57 47 100% 84 71 300% 152 132 500%246 211 Ultimate Tensile Strength 4719 4282 (psi) Increase in TensileStrength 10.2% — (Ex. 4 vs Comp. Prep. D) Ultimate Percent 1066 1094Elongation (%) Tear Strength (kN/m) 26.2 17.5 Increase in Tear Strength49.7% — (Ex. 4 vs Comp. Prep. D)

As will be apparent from the preceding tabulation, Example 4 (utilizingMDNO and sulfur as the crosslinking agents but free of accelerator andSBR reinforcing agent) exhibits superior tensile and tear properties ascompared with Comp. Prep. D. (utilizing a peroxide and sulfur ascrosslinking agents, but otherwise identical). Moreover, notwithstandingthe increase of tensile and tear properties, the tensile modulus valuesremained low.

Comparison of Natural Rubber Films Crosslinked with MDNO (Examples 5-6)with Natural Rubber Films Crosslinked with Dicumyl Peroxide (ComparativePreparations E-F)

EXAMPLE 5 Comparative Preparation E Comparison of Natural Rubber LaticesPlus an SBR Reinforcing Agent Cured with MDNO (Example 5) and DicumylPeroxide (Comp. Prep. E) Crosslinking Agents

TABLE 9 MDNO and Peroxide-Cured Natural Rubber Films Example 5 Comp.Prep. E Parts by Parts by Weight Weight Ingredient % TSC (Dry) % TSC(Dry) Centex HF NRL 61.3 100 61.3 100 Styrene Butadiene Rubber Latex52.4 5 52.4 5 (SBR) MDNO Dispersion 30 1.4 — — Dicumyl Peroxide Emulsion— — 37 1.4 Darvan WAQ surfactant 30 0.5 30 0.5 Cab-O-Sperse GP-50Aqueous 20 2 20 2 Silica Dispersion Antioxidant Dispersion 50 2 50 2Deionized Water - as necessary to dilute compound to 45% TSC

TABLE 10 Comparison of Tensile Properties of MDNO and Peroxide CuredNatural Rubber Films Property Example 5 Comp. Prep. E Tensile Modulus 50% 74 70 100% 112 112 300% 273 304 500% 1084 1235 Ultimate TensileStrength 5463 4141 (psi) Increase in Tensile Strength 31.92% — (Ex. 5 vsComp. Prep. E) Ultimate Percent 820 666 Elongation (%) Tear Strength(kN/m) 41.1 13.1 Increase in Tear Strength 213.7% — (Ex. 5 vs Comp.Prep. E)

As will be apparent from the preceding tabulation, Example 5 (utilizingnatural rubber and an MDNO crosslinking agent with a conventional SBRreinforcing agent but free of accelerator) exhibits superior tensile andtear properties as compared with Comp. Prep. E (utilizing natural rubberand a peroxide crosslinking agent, but otherwise identical). Moreover,notwithstanding the increase of tensile and tear properties, the tensilemodulus values remained low.

EXAMPLE 6 Comparative Preparation F Comparison of Natural Rubber LaticesCured with MDNO (Example 6) and Dicumyl Peroxide (Comp. Prep. F)Crosslinking Agents

TABLE 11 MDNO and Peroxide-Cured Natural Rubber Films Example 6 Comp.Prep. F Parts by Parts by Weight Weight Ingredient % TSC (Dry) % TSC(Dry) Centex HF NRL 61.3 100 61.3 100 MDNO Dispersion 30 1.4 — — DicumylPeroxide Emulsion — — 37 1.4 Darvan WAQ surfactant 30 0.5 30 0.5Cab-O-Sperse GP-50 Aqueous 20 2 20 2 Silica Dispersion AntioxidantDispersion 50 2 50 2 Deionized Water - as necessary to dilute compoundto 45% TSC

TABLE 12 Comparison of Tensile Properties of MDNO and Peroxide CuredNatural Rubber Films Property Example 6 Comp. Prep. F Tensile Modulus 50% 56 56 100% 82 91 300% 158 212 500% 471 604 Ultimate TensileStrength 4857 3893 (psi) Increase in Tensile Strength 24.8% — (Ex. 6 vsComp. Prep. F) Ultimate Percent 907 718 Elongation (%) Tear Strength(kN/m) 32.8 13.0 Increase in Tear Strength 152.3% — (Ex. 6 vs Comp.Prep. F)

As will be apparent from the preceding tabulation, Example 6 (utilizingMDNO as the crosslinking agent but free of accelerator) exhibitssuperior tensile and tear properties as compared with Comp. Prep. F(utilizing a peroxide as crosslinking agent, but otherwise identical).Moreover, notwithstanding the increase of tensile and tear properties,the tensile modulus values remained low.

EXAMPLE 7 Influence of a Maturation Period on Physical Properties ofFilm Product of Example 1

This example illustrates test films prepared from the aqueous latex ofExample 1, but with a maturation period of 24 hours at room temperatureprior to formation of the films. A comparison of the tensile propertiesof the test films prepared with (Comp. Prep. G) and without (Example 1)a maturation period are shown in Table 13.

TABLE 13 Demonstration of Undesirable Pre-vulcanization from Maturation.Ultimate Modulus Values (PSI) Tensile Ultimate Tear 50% 100% 300% 500%Strength (PSI) Elongation (%) Strength (kN/m) Example 1 66 91 164 2574911 1124 36.2 Comp. Prep. G (Films 62 92 168 270 2179 995 18.3 preparedafter 24 hours standing at room temperature)

EXAMPLE 8 Dental Dams Formed by Casting Techniques

Dental dams were formed from the compounds used in Examples 1 and Comp.Prep. C. Rather than being dip-molded, as in Example 1, the dental damswere formed by casting the compounded latex onto thin flat sheets ofstainless steel. The dental dams were vulcanized by essentially the samemethod as that of Example 1. The resulting dental dams were compared fortaste and odor. The rubber dam made with the formulation of ComparativePreparation C had an odor and a detectable taste. The rubber dam madefrom the formulation of Example 1 did not have any detectable taste orodor.

EXAMPLES 9-11 Condom Films Prepared by Imbibition

A batch of latex was compounded as described in Example 1, except thatMDNO was eliminated from the formulation. Latex condom shaped films wereprepared by the same method as that of Example 1. Upon drying, thecondom film was not vulcanized. Instead, a dry gel of syntheticpolyisoprene compound was deposited on the former.

A solution containing 1% by weight MDNO and 99% by weight toluene wasprepared. Immediately after removal from the drying oven, the dry gel onthe closed end of the condom former was immersed in the toluene/MDNOsolution. The film was allowed to dwell in this solution for 60 seconds,after which it was removed.

It was apparent that the solution had swelled, but not dissolved therubber. The condom former was then placed in a hot air oven set to 150°F. for one hour to drive off the toluene and promote the vulcanizationof the rubber. The former was allowed to cool down to room temperature,and the condom was removed from the former.

This procedure was repeated two more times, forming three films fortensile testing (Examples 9-11). Table 14 shows the results of thephysical property testing, per ASTM D-3492.

TABLE 14 Tensile Properties of Condoms from MDNO Imbibed PolyisopreneTensile Results 100% 300% 500% Ultimate 50% Modulus Modulus ModulusModulus Tensile Ultimate Values Values Values Values Strength PercentExample (PSI) (PSI) (PSI) (PSI) (PSI) Elongation  9 73 103 194 324 40781049 10 75 104 199 341 5036 1058 11 78 118 226 397 5172 1003 Median 75104 199 341 5036 1049 Values

The film products of Examples 9-11 were transparent, and devoid oftaste, odor and color.

EXAMPLES 12-13 Polyisoprene Condoms Formed from Pre-Cooled RubberCompound

Two batches of synthetic polyisoprene latex were compounded as describedin Example 1. Multiple sets of latex condoms were prepared by the samemethod as that of Example 1 at time intervals of 0.75 hours, 7.5 hours,24.5 hours, and 31.5 hours, all in relation to initial time (t=0)corresponding to formulation time.

During the time intervals between the film preparation of the respectivefilm products, one batch of latex was stored at room temperature and thesecond was stored in a bath of ice and water at approximately 0° C. Oncedipped, the films were processed in the same manner as Example 1.

This technique was utilized to produce films for tensile testing. Theannexed FIGURE and tables 16 and 17 show the results of physicalproperty testing, per ASTM D3492, as a function of preparation time. Asmay be seen, placing the formulated latex into an ice bath prior to useis an effective way to slow down the pre-vulcanization of the compoundedlatex. It is clear that pre-vulcanization occurs in the liquid latex bynoting the continually increasing 100% modulus value of the testspecimens cut from the resulting condoms, which is an indicator ofoverall cure levels. However, the tensile strengths of the test filmsfrom the condoms drop over time, due to the undesirable nature ofpre-vulcanization.

TABLE 16 Physical Property Data for Rubber Compounded at 0° C. (Example12) Latex Aged in Ice Bath Time Interval after Modulus Values (PSI)Ultimate Tensile Ultimate Percent compounding (hours) 50 100 300 500Strength (PSI) Elongation (%)  0.75 58 84 155 241 4961 1168 (Baseline) 7.5 60 85 155 247 3739 1106 24.5 58 85 152 239 3334 1109 31.5 57 83 153241 2939 1086

TABLE 17 Physical Property Data for Rubber Compounded at 25° C. (Example13) Latex Aged at Room Temperature Time Interval after Modulus Values(PSI) Ultimate Tensile Ultimate Percent compounding (hours) 50 100 300500 Strength (PSI) Elongation (%)  0.75 58 84 155 241 4961 1168(Baseline)  7.5 59 86 161 256 3312 1078 24.5 64 91 164 264 2112 987 31.567 99 176 276 2107 991

EXAMPLE 14 MDNO Addition in a Coagulant Bath

A batch of latex was compounded as in Example 1, except that MDNO waseliminated from the formulation. A 10-20% calcium nitrate coagulant bathwas prepared with 0.5% Igepal CO-630 surfactant and 1.0-3.0% MDNO.

Latex condoms were prepared by the same method as that of Example 1.except that the coagulant provided the source of MDNO. This method isadvantageous because the MDNO is separated from the rubber until therubber is processed.

EXAMPLE 15 Post-Drying Coagulant Dip

An additional example utilizing MDNO in the coagulant involves a postlatex coagulant dip. The same procedure from above was used except thatupon removal from the latex tank the formers were dried for 5 minutes ina 150° F. oven and readied for an additional coagulant dip with MDNO.

The additional coagulant dip was conducted post-latex preparationutilizing a similar dipping profile as that used in the first coagulantdip. Condom formers were then placed in a 150° F. oven for 1 hour,leached for approximately 5 minutes in a 55° F. water bath and dried.This method produces a more evenly cured film than Example 14.

EXAMPLE 16 Multiple Coagulant/Latex Dipping Techniques

An additional example, applying MDNO in the coagulant involves two ormore coagulant and latex dip combinations. The following table shows theresults for physical property testing, per ASTM D-3492.

TABLE 18 Physical Property Data for Multiple Coagulant Dips FilmProperties Values Modulus @ 50% Elongation (psi) 44 Modulus @ 100%Elongation (psi) 68 Modulus @ 500% Elongation (psi) 142 Median TensileStrength (psi) 2286 Percent Elongation (%) 1331 Average Swell Percent(%) 94.0

EXAMPLE 17 Straight Dip Molding Method with MDNO Bath

A batch of latex was compounded as in Example 1, except that MDNO waseliminated from the formulation and no deionized water was added. A0.5-3.0% MDNO bath was prepared by adding an MDNO dispersion todeionized water. Latex condom-shaped films were prepared via thestraight dip molding method.

Formers were dipped into the MDNO bath and dried for 5 minutes in a 150°F. oven or until dry. The formers were cooled before being dipped intothe latex. Latex films were then roll dried and placed in a 150° F.oven. This technique was repeated until the desired film thickness wasachieved. Formers were dipped into the MDNO bath for a final dip anddried for 1 hour in a 150° F. oven or kept at room temperature for 24hours for curing.

EXAMPLE 18 Straight-Dipping in an Organic Solvent Bath

MDNO was dissolved in a suitable solvent in 0.5-3.0% concentration.Latex condom-shaped films were prepared via the straight dip moldingmethod of Example 17 except using a solvent-based bath.

EXAMPLE 19 Casting Alternating Layers of Rubber and MDNO

A batch of latex was compounded as in Example 1, except that MDNO waseliminated from the formulation. Films were prepared by alternatinglayers of MDNO and rubber. A layer of an MDNO dispersion or MDNOdissolved in solvent was cast in a tray and then dried in al 50° F. ovenfor 5 minutes. Latex was then coated over the MDNO and dried in a 150°F. oven for 5 minutes. This procedure was repeated until desiredthickness was achieved. Films were cast with an additional layer of MDNOand dried for 1 hour in a 150° F. oven or kept at room temperature for24 hours for curing.

EXAMPLE 20 Solvent (Non-Latex) Casting Method

A solvent-based rubber system was prepared by dissolution of rubber in asuitable solvent to a concentration of 10-20% solids. MDNO dissolved ina solvent was cast in a tray then dried in a 150° F. oven for 5 minutes.A rubber solution was then coated over MDNO and dried in the 150° F.oven for 5 minutes. This procedure was repeated until the desiredthickness was achieved. Films were cast with an additional layer of MDNOand dried for 1 hour in a 150° F. oven or kept at room temperature for24 hours for curing.

EXAMPLE 21 Procedure For Dipping Surgical Glove, Examination Glove,Catheter Balloon, Infuser Balloon, or Breathing Bag

A synthetic polyisoprene latex was formulated as in Example 1. Theformulation was rolled for 15-30 minutes prior to use.

Products, including surgical gloves, examination gloves, catheterballoons, infuser balloons and breathing bags were prepared via thecoagulant dip molding method. Mandrels were heated to 150° F. beforebeing dipping into the coagulant. The mandrels were dried for 5 minutesin a 150° F. oven and dipped into the latex solution. The formers weredried for 5-10 minutes in the 150° F. oven and leached for 3 minutes ina 131° F. water bath. The formers were dried for 1 hour in the 150° F.oven or kept at room temperature for 24 hours for curing.

The products were stripped with the use of powder. All products werefully vulcanized and functional.

EXAMPLE 22 Latex Gloves Formed by Continuous Dipping

Synthetic polyisoprene latex was prepared by the same method as that ofExample 1 for a continuous glove dipping operation. As glove formers areprocessed through the dipping tank, a measurable quantity of latex isremoved. Newly compounded latex is continually added into the dippingtank in quantities that closely or nearly equal the amount of latex thatis being removed on the glove dipping formers.

This technique keeps the volume of latex in the dipping tank nearlyconstant, while continually replacing aging latex. In doing so, thelatex in the dipping tank is refreshed at a given rate, keeping theresidence time for the compounded latex very short, allowing for only asmall amount of pre-vulcanization.

The glove made in this example is a standard size 6½ latex surgicalglove which has a weight of about 12.5 grams. The volume of latex, at45% total solids content (TSC), used to produce this glove is 30 mL.

In the example, 30 mL of latex is added to the dipping tank for eachdipped glove former that is removed from the tank. Once dipped, theglove former proceeds along the glove-dipping machine, which carries outthe essential latex article processing steps described in Example 1. Atthe end of the line, the glove is stripped from the former and theresulting glove is fully vulcanized with excellent properties.

A dipping tank that can accommodate 25 glove formers at any given timehas dimensions of 20″ wide by 20″ long with a height of 12″. This tankhas a filled volume of 4800 in³. Given this volume, each former dippedremoves 0.0375% of the total volume. At this rate, one tank volume worthof latex is used for every 2667 glove formers dipped. 100 glove formersare dipped per minute resulting in one tank volume being added every 27minutes. Accordingly, for every 2.3 tank volumes removed andreplenished, only 10% of the original volume of latex remains. Thistranslates into 90% of the original latex being removed every 62minutes. This prevents the latex from reaching an unacceptable state ofpre-vulcanization.

As shown in Table 19, the average age of the latex in the tank reachessteady state conditions after about 248 minutes (4 hours), and remainsindefinitely at an average age of 37.89 minutes.

TABLE 19 Average Latex Age in Dipping Tank Time Average Age (minutes)(minutes) 0 0.00 62 34.10 124 37.51 186 37.85 248 37.89 310 37.89 37237.89 434 37.89 496 37.89 558 37.89 620 37.89

EXAMPLE 23 Alternative Continuous Dipping Operation

A continuous glove dipping operation is performed as in Example 22except that the latex compound used for the continuous dipping operationdoes not contain MDNO.

Uncompounded latex is added on a continuous or intermittent basis, andan MDNO dispersion is added separately. The MDNO may also be added on acontinuous or intermittent basis so as to keep a constant and optimalratio of MDNO and uncompounded latex in the dipping tank.

EXAMPLE 24 Addition of Microencapsulated MDNO to a Latex Compound

The addition of microencapsulated MDNO particles to a latex compoundwill allow for controlled release of the MDNO, which will extend theuseful lifetime of the latex.

The MDNO microencapsulated particles are prepared by making a 50% MDNOin wax solution. 50.0 g of paraffin wax is heated to 150° F., and then50.0 g of MDNO is added. The solution is stirred until all of the MDNOdissolves. The wax is cooled and ground up into small particles.

A 15% MDNO wax dispersion is prepared by combining 90.0 g of the 50%MDNO in wax solution, 3.1 g of Darvan # 1, 2.4 g of Van Gel B (aprocessed magnesium aluminum silicate available from Vanderbilt ChemicalCompany, Norwalk, Conn.) 0.7 g of Igepal CO-630, and 204.0 g ofdeionized water. All ingredients are mixed on a ball mill for 3 hours.The latex is compounded as described in Example 1, except that 1.2 phrMDNO is added in the form of microencapsulated particles. The latexfilms are prepared by heating mandrels to 150° F. and dipping into thecoagulant. The mandrels are dried for 5 minutes in a 150° F. oven anddipped into the latex solution. Films are dried for 5-10 minutes in a150° F. oven and leached for 3 minutes in a 131° C. water bath. Thefilms are dried for 1 hour in a 150° F. oven.

The elevated temperature allows for a controlled release of the MDNOfrom the wax to begin the curing process. The films are then strippedwith powder and readied for tensile testing. The dipping procedure isrepeated each day to show the aging properties of the latex. The latexformulation is stored in an ice bath and rolled for 15 minutes prior todipping.

Table 20 shows the expected result for latex films formulated withmicroencapsulated MDNO.

TABLE 20 Expected Physical Properties of Microencapsulated MDNO LatexFilms. Control: Days Latex Aged MDNO Dispersion Microencapsulated MDNO 04960 psi 4960 psi 1 3940 psi 4960 psi 2 3230 psi 4960 psi 22 1740 psi4960 psi

As can be seen from the foregoing description, it is very clear thatpolynitrile oxide can be used in accordance of the present invention toproduce both natural rubber and synthetic polyisoprene dip-molded filmproducts, which have superior tensile strength, tear strength, andelongation properties.

The present invention is not limited in scope by the specificembodiments described herein. Indeed, various modifications of theinvention in addition to those described herein will become apparent tothose skilled in the art from the foregoing description and theaccompanying figures. Such modifications are intended to fall within thescope of the appended claims. It is further to be understood that allvalues given in the foregoing examples are approximate, and are providedfor purposes of illustration.

Patents, patent applications, publications, product descriptions, andprotocols which are cited throughout this application are incorporatedherein by reference in their entireties for all purposes.

1. (canceled)
 2. (canceled)
 3. (canceled)
 4. (canceled)
 5. (canceled) 6.(canceled)
 7. (canceled)
 8. (canceled)
 9. (canceled)
 10. A method forforming dip-molded or cast thin walled rubber film products comprised ofnatural rubber or synthetic cis-1,4-polyisoprene rubber crosslinked witha polynitrile oxide crosslinking agent, comprising: (a) compounding anatural rubber or synthetic cis-1,4-polyisoprene rubber so as tosubstantially reduce or prevent pre-vulcanization of the resultingrubber compound; (b) dip-molding or casting the rubber compound to formthe thin-walled rubber film product; (c) admixing the rubber compound orthin walled film product with at least one polynitrile oxidecrosslinking agent; and (d) curing the rubber compound to producecrosslinking therein.
 11. The method of claim 10, wherein thepolynitrile oxide crosslinking agent is admixed with the rubber compoundin step (a).
 12. The method of claim 10, wherein the rubber compounddoes not contain a sulfur-containing accelerator or nitrosatablesubstance.
 13. The method of claim 10, wherein the crosslinking agentcomprises mesitylene dinitrile oxide (MDNO) or 2,4,6-triethylbenzenedinitrile oxide (TON-2).
 14. The method of claim 10, wherein the thinwalled film product is formed by dip-molding a rubber latex.
 15. Amethod according to claim 10 wherein the rubber compound is cured at atemperature of about 150° F. or less.
 16. The method of claim 10,wherein pre-vulcanization is substantially reduced or prevented by (i)reducing the temperature of the compounding ingredients in step (a) tobelow about 25° C.; or (ii) forming a microencapsulate containing thepolynitrile oxide prior to compounding; or (iii) compounding the latexwith the polynitrile oxide immediately prior to curing; or (iv) imbibingthe polynitrile oxide into a wet or dry rubber gel; or (v) placing thepolynitrile oxide in a coagulation bath; or (vi) curing the rubbercompound by applying and curing alternating layers of the rubber and thepolynitrile oxide; or (vii) adding freshly compounded rubber to adip-molding chamber and dipping a plurality of formers in the rubbercompound and curing the rubber thereof; or (viii) substantially reducingor eliminating a maturation period for the compounded rubber.
 17. Themethod of claim 16, wherein pre-vulcanization is substantially reducedor prevented by forming a microencapsulate containing the polynitrileoxide prior to compounding.
 18. The method of claim 16, whereinpre-vulcanization is substantially reduced or prevented by imbibing thepolynitrile oxide into a wet or dry rubber gel.